A database is a collection of logically related data arranged in a predetermined format, such as in tables that contain rows and columns. To access the content of a table in the database, queries according to a standard database query language (such as the Structured Query Language or SQL) are submitted to the database. A query can also be issued to insert new entries into a table of a database (such as to insert a row into the table), modify the content of the table, or to delete entries from the table. Examples of SQL statements include INSERT, SELECT, UPDATE, and DELETE.
There can be diverse types of workloads that can execute in a database management system. Some workloads may include low priority requests, such as background load requests or reporting requests. Another type of workload can include requests that are relatively complex. Yet other workloads include requests that have short durations but very high priorities. Yet another type of workload includes continuous or batch requests, which run for a relatively long time.
Conventional database management systems do not properly respond to various internal or external events that may impact performance of the various different types of workloads that may be concurrently running in the database management system. Examples of such internal or external events include unforeseen events (e.g., request volume surge, exhaustion of shared resources, component outages) or even planned situations (e.g., systems maintenance or data load). Also, conventional database management systems fail to properly consider the impact of inaccurate estimates provided by an optimizer in the database system on whether or not the database management system would be able to meet service level goals associated with the workloads.